WO2012/063074 describes building a column of stack bonded hollow concrete blocks which are filled with reinforced concrete to form a reinforced concrete core. A cleat is fixed to a foundation, floor slab, beam or like pre-existing load bearing structure in a position at the base of where it is desired to erect the column. Bolts, expansion bolts or other appropriate fasteners are used for such fixing, passing through holes in a base plate of the cleat. A pair of terminal rebars is then fitted to the cleat by engaging tubular sockets welded to their ends over a corresponding pair of spigots upstanding from the cleat base plate. A bed of mortar or like jointing material is spread around the base of the cleat. A hollow block is then laid in the mortar in the correct position to form the first course of encasing masonry for the column. The upper rim of the block just laid is spread with a layer of mortar and the next block is laid in stack bond on top of it. Further blocks are laid similarly in succession until only just sufficient length of each terminal rebar protrudes above the top block to form a lap joint with a length of plain rebar (or other elongate reinforcement) which is to be joined to the projecting rebar upper end. Once the lap joints have been secured e.g. by wire ties or the like, further hollow blocks can be laid in stack bond, threaded over the tops of the plain rebars. Further lengths of plain rebar (or other elongate reinforcement) can be secured by lap joining until the desired height of the column is reached. The cavity enclosed by the stacked hollow blocks can be filled with concrete or other cementitious material at suitable intervals as block laying progresses. If desired, alternate courses may be formed using two separate halves of a hollow block, so that the pointing pattern of the column blends with that of an adjacent panel of blockwork, apart from the discontinuity formed by an expansion joint interposed between the column and the panel. Additionally or alternatively, one or both sides of the reinforced concrete filled blockwork column may be keyed/bonded to the adjacent blockwork panel; adjacent courses of blocks being laid in staggered relationship with each other, e.g. so that a stretcher bond pattern in the panel extends into the reinforced concrete filled column. Such structures are described in WO2009/098446.
These building methods require skilled labour to carry them out. A particular difficulty arises when thin walled blocks are used, as is preferred, in order to maximise the cross-section and hence the strength of the reinforced concrete core of the blockwork column. The upper rim of such hollow blocks is quite narrow (as little as 20 mm wide) and it is therefore difficult to spread an even layer of mortar on this rim, upon which to lay the next block to form the column. Mortar is easily dislodged or dropped into the hollow interior of the column. This not only is a waste of mortar, but may also contaminate and weaken the reinforced concrete filling or its bond to the foundation. A supplementary problem arises in that every block used to form the column must be lifted over the upper ends of the rebars and then treaded back down the rebars to its final position. This extra lifting and lowering of masonry units is physically demanding. Joining successive lengths of rebar as the height of the column increases is also rather time consuming.